Properties of Lenses and Focal Length
Plus lens
This condition can be attributed to the cornea being more oval shaped than circular resulting in two focal points
Astigmatism
This is the curve around which all other curves are based
Base Curve
This designation describes the density of a material and it's relationship to light dispersion
Abbe Number
This was the first material used for lenses
Glass
This lens produces a virtual image
Minus Lens
This ongoing condition resulting in the thinning of the cornea causing a bulge known as a "cone" and may eventual require a corneal transplant is?
Keratoconus
This is the formula that demonstrates the relationship between the front and back curves of the lens to achieve the final prescription
Nominal Lens Formula
This designation describes the weight of a material
Specific Gravity
This material was developed by the military and is known for its low specific gravity and tensile strength
Trivex
This lens increases in power as it moves away from the eye
Plus lens
This condition of the eye is the result of the meridians being greater or less than 90 degrees
irregular astigmatism
Vogels rule states that for plus spherical lenses you must?
Add +6.00D
This designation describes the behavior of light as it moves through a material and the way it will bend or refract.
Index of Refraction
This material is incredibly dense and therefore lenses made with it can be thin but often requires anti-reflective coatings
Hi-Index Plastic
This lens decreases power as it moves away from the eye
Minus Lens
This diagram is used to show the two main meridians and the cylinder power
Optical Cross
To achieve the base curve of a spherocylinder lens what is the first thing you need to do after you transpose the prescription?
Get the spherical equivalent
This material has an index of refraction of 1.53
Crown Glass
This process involves molten salt and results in an ion exchange which results in a strong bond between glass molecules
Chemical Tempering
The focal length in cm of a 50D lens is?
2cm
Opticians and Optometrists must transpose prescriptions given by Ophthalmologists into the following type of prescription format
Minus Cylinder Format
The best base curve for the following Rx is?
-4.00 -2.00 x 180?
+3.50
This material has the lowest Abbe value
Hi-Index Glass
This element is used to tint glass and turns red when it cools
Gold